Manufacture of ketenes



Patented a. 10,- 1939 I a 2,175,811

UNITED STATES PATENT OFFICE MANUFACTURE or KETENES Donald J. Loder, Wilmington, Del., assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware- No Drawing. Application October 28, 1936,

Serial No. 108,005

19 Claims. (Cl. 260-550) This invention relates to a process for the spectively. These terms are used since the mechmanufacture of ketenes and more particularly anism of the reaction appears to be, in most to a process for the manufacture of ketenes by instances, that as the ester decomposes an alcothe thermal decomposition of aliphatic carho] is split off leaving the ketene or substituted boxylic acid esters. ketene.

The industrial pyrolysis of acetone to acetic The esters which may be used in the process anhydride and ketene is well known, as well as of the present invention are primarily the allthe similar treatment of acetaldehyde and alkyl phatic monocarboxylic acid esters of the aliphatic ketones generally to produce ketene or substimonohydric alcohols, such, for example, as methyl tuted ketenes. These processes, however, have acetate, ethyl acetate, 'propyl acetate, isobutyl 10 not been attractive from the commercial standacetate, and the higher esters of acetic acid with point for the primary reason that the raw ma- 4 straight or branched chain aliphatic saturated terials have been obtainable only at high cost or unsaturated alcohols, of these esters methyl and the ketenes produced therefrom only in unacetate decomposes to ketene and methanol much economical yield. more readily and efllciently than do the higher 15 An object of the present invention is to proester to their corresponding products. Not only vide a process for the preparation of ketenes by can esters of acetic acid be thermally decomposed the thermal decomposition of organic esters. in accord with the process of this invention to Another object of the invention is to provide a give ketene, but likewise the higher aliphatic .process wherein ketenes generally, such, for exacid esters may be treated to give substituted 20 'ample,'as ketene, methyl ketene, diethyl ketene, ketenes. For example, when methyl propionate and the like, may be prepared by dehydroalis dehydromethoxylated, a methyl ketene and koxylating appropriate esters of the carboxylic methanol will be the major products; when ethyl acids. A more specific object is to provide a isobutyrate is dehydroethoxylated, dimethyl keprocess for the preparation of ketene by thertene and ethanol will be the major reaction prod- 25 mally decomposing methyl acetate. A still more ucts. Accordingly, in a substantially analogous specific object is to provide a process wherein manner, other substituted ketenes may be promethyl acetate is passed at elevated tempera.- duced from the higher monocarboxylic acid estures and subatmospheric pressures over a cataters of the straight or branched chain type alcolyst which accelerates the thermal decomposihols. Generally speaking the methyl esters of 30 tion of the ester into ketene and methanol. Other the higher acid ester acylates give the substituted objects of the invention will hereinafter appear. ketenes and alcohols more readily than do the The above objects are realized by subjecting in higher alkyl esters of the corresponding acids. the vapor phase an aliphatic carboxylic acid ester While usually the monocarboxylic acid esters may to comparatively high temperatures and prefbe thermally decomposed to ketenes much more 35 erably pressures somewhat lower than atmosreadily than polycarboxylic acid esters, neverpheric. With these conditions, under which the theless, the latter type esters, and more particureaction is preferably accelerated in the presence larly the di and tricarboxylic acid esters, can be 'of a suitable catalyst, the ester is decomposed to treated in accord with the process herein de- 40 give ketene and an alcohol. In many instances, scribed to produce valuable compounds. 40 owing to the high reactivity of the ketene, it The process is preferably conducted in the may react with the products formed, such as, vapor phase, the ester is vaporized either prior water and the alcohol produced, to give, in adto or during the reaction, and is thermally dedition to the ketene and alcohol, acids and ancomposed at a temperature of from approximately hydrides. In order, however, to control the di- 500 to 1000 C. and preferably from 6 C- rection of the reaction and obtain the desired in the presence of a suitable type catalyst, such, product, namely, ketene, various expedients are for example, as sodium meta phosphate, silica resorted to which will be more fully described gel or silica gel supporting a suitable promoter hereinafter. such as phosphoric acid or hydrated or anhydrous 50 When reference is made to dehydroalkoxylatboron oxide and like dehydrating catalysts. 50

- ing, dehydromethoxylating, and the like, in the It has been found that the reaction proceeds,

specification and claims appended hereto, it will particularly when methyl .acetate is being therbe understood that these terms will connote the mally decomposed to ketene, at subatmospheric removal from the ester of an zilkoxy group and pressures preferably ranging between 10 and 700 65 hydrogen or a methoxy group and hrdrogen, remm., with space velocities ranging between 500 and 10,000 under these pressures. (The space velocity is the number of unit volumes of gas, at standard conditions, passing per hour through a unit volume of the catalyst.)

In order to inhibit the decomposition of the ester of valueless by-products the presence of water vapor has proved to be remarkably effective. For example, it amounts of up to 8% are introduced with the ester, it has been found that while the yields of ketene continue to be high, a much larger part of the ester decomposed in the absence of water vapor is converted to a usable product, namely, the acid corresponding to the ester used. Higher amounts are not usually advisable because of greater dilution of the product.

Catalyst, temperatures, and space velocity are more or less interdependent, that is, to avoid undue decomposition, an increase of temperature requires, for optimum results, a like increase in space velocity. As is usual in chemical reactions the higher the temperature the more favorable the reaction rate, and accordingly in this reaction also when high temperatures are employed, in which reaction rates are high, comparatively high space velocities should be employed. It has been found that to limit side reactions it is advisable to operate at diminished pressures, and pressures around 100 mm. of mercury or lower have generally produced optimum operating conditions, although at higher pressures decreased yield of ketene is partially compensated for by increased conversion to the acid corresponding to the ester trea I shall now describe by way of examples methods for carrying into practice my invention but it will be understood that the details therein given will not limit in any way the scope of the inventlon.

Example I Example I I A copper lined catalyst tube was filled with silica gel and into it 1.13 mols of methyl acetate was injected at a space velocity of approximately 1,680. The catalyst chamber was maintained at a temperature between 507 and 530 C. with a pressure of approximately 1'70 mm. A yield of approximately 64% ketene was realized. The yields are calculated on a molal basis as a percentage of that theoretically obtainable.

Example III Into a catalyst tube containing boric acid or silica gel approximately 1.14 mols 6! liquid methyl acetate was injected at a space velocity of 2,040. The converter was maintained at a temperature of between approximately 525 and 635 C. and the pressure within the converter at approximately 180 mm. Approximately 87.8% yield of ketene was found.

Example IV .ing between 500 and 650 C. and the pressure within the converter at approximately 90 mm.

Example V Into a copper converter containing no catalyst approximately 0.315 mol of liquid methyl acetate was injected. The converter was heldat a temperature of approximately 763 C. and its contents at approximately 28 mm. pressure. A 21.5% yield of ketene was obtained.

Various methods may be employed for recovcry of the ketene, e. g., compressing the gaseous products and scrubbing the thus compressed products with acetone or methyl acetate or if desired the ketene may be absorbed, without the necessity of the compression step, directly in acetic acid.

From a consideration of the above specification it will be appreciated that many changes may be made in the details therein given with out departing from the invention or sacrificing any of the advantages that may be derived therefrom.

. I claim:

l. A process for the preparation of a ketene which comprises thermally decomposing, in the vapor phase, a lower alkyl ester of a lower aliphatic monocarboxylic acid at a temperature ranging between approzn'mately 500 and approximately 1000 C.

2. The process according to claim 1 conducted under pressures lower than atmospheric.

3. The process according to claim 1 conducted by contacting the ester of the aliphatic carboxylic acid with a silica gel catalyst.

4. The process according to claim 1 in which the ester of the aliphatic carboxylic acid is contacted with boric oxide supported on silica gel.

5. A process for the preparation of ketene which comprises thermally decomposing, in the vapor phase, a methyl ester of a mono-basic lower aliphatic acid at a temperature between approximately 500 and approximately 1000 C.

6. A process for the preparation of ketene which comprises thermally decomposing, in the vapor phase, a methyl ester of a fatty acid at a temperature between 500 and 1000 C., a pressure of less than one atmosphere and in the presence of silica gel as the catalyst.

7. A process for the preparation of ketene which comprises thermally decomposing, in the vapor phase, methyl acetate at a temperature between approximately 500 and approximately 1000 C.

8. A process for the preparation of ketene which comprises thermally decomposing, in the vapor phase, methyl acetate in the presence of a silica gel catalyst.

9. A process for the preparation of methyl ketene which comprises thermally decomposing, in the vapor phase, methyl propionate at a temperature of approximately 500 and approximately 1000 C.

10. A process for the preparation of methyl ketene which comprises thermally decomposing,

in the vapor phase, methyl propionate in the presence of a silica gel catalyst.

11. A process for the preparation of ketene 16. The process of claim I conducted in the which comprises thermally decomposing, in the 'vapor phase, an ester of an aliphatic carboxylic 'acid by contacting-it with a dehydrating catalyst.

12. A process for the preparation of ketene which comprises contacting methyl acetate with a silica gel catalyst at a temperature of from 500 to 1000 (2., under a pressure of from 10 to 700 mm. and a space velocity of 500 to 10,000.

13. A process for the preparation of ketene which comprises. contacting methyl acetate with a silica gel catalyst promoted with boric oxide at a temperature ranging between 650 and 800 C.

14. The process of claim 13 conducted under a pressure ranging between 10 and 700. mm.

15. The process of claim 13 conducted at a space velocity ranging between 1,000 and' 10,000.

presence of water vapor.

17. The process or claim 13 conducted in the presence of water vapor.

18. A process for the preparation of ketene 5 which comprises thermally decomposing methyl acetate in the presence of from 2 to 8% water vapor based on the ketene present at a temperature ranging between 500 and 1000 C.

19. A process for the preparation of ketene which comprises contacting methyl acetate with a silica gel catalyst promoted with boric oxide at a temperature ranging between 506 and 631 0., a pressure of approximately 114 mm. and a space velocity of approximately 1400.

DONALD LIT. Lonn'a. 

